Bariatric surgery induces long-term changes on the gut metagenome contributing to fat mass regulation

Bariatric surgery is the most effective procedure for the treatment of obesity. Given the role of the gut microbiota in regulating host metabolism and adiposity, we investigated the long-term effects of bariatric surgery on the human gut metagenome in patients randomized to Roux-en-Y gastric bypass and vertical banded gastroplasty. Genera of the Proteobacteria were specifically enriched after bypass, and the abundance of genes for fatty acid metabolism, nitrogen metabolism and two-component systems was increased after both procedures nine years after surgery. Through colonization of germ-free mice with stools from the patients we demonstrated that the altered gut microbiota promoted reduced fat deposition in recipient mice. Recipients of bypass microbiota also had a lower respiratory quotient, indicating decreased utilization of carbohydrates as fuel. Our results suggest that the gut microbiota may play a direct role in the reduction of adiposity observed after bariatric surgery.